In engines for alternative fuels, the increasing need for ignition voltage and increased spark-plug wear are a growing problem. Engines powered by alternative fuels need a varying amount of ignition voltage and energy of the spark, depending on the fuel used. There are also engines with variable EGR (Exhaust Gas Recirculation) and in case of high EGR, the ignition of the fuel mixture is more difficult and requires a high-energy spark. To achieve ignition, the ignition parameters such as ignition voltage, spark burn time and peak current of the spark are often maximised, causing substantial wear of the spark plugs. Furthermore, the burn time of the spark is affected by turbulence and pressure in the combustion chamber, and if the current of the spark is too low it can go out by itself, making the release of a new spark necessary, which also results in considerable wear. Another parameter that affects spark-plug wear is the polarity of the spark.
U.S. Pat. No. 7,347,195 discloses a method to control the current to a spark plug to enable control of the intensity and/or duration of an ignition spark. The system enables a spark during a predetermined burn time, to individually adapt the ignition current to the current operating mode of the engine or to external conditions such as fuel quality and/or weather. The system comprises a first and a second circuit, the first circuit being a conventional inductive ignition system, and the second circuit including a control circuit connected to a second side of the ignition coil to control the duration and current of a spark.
U.S. Pat. No. 6,189,522 discloses an ignition system comprising an ignition coil to simultaneously ignite a pair of spark plugs. The system further comprises a switch which, when assuming an operating mode, causes the first spark plug to generate a negative spark and the second spark plug to generate a positive spark. When another operating mode is assumed the opposite happens: the spark plugs switch polarities.